b: =100x1000=100000

a)=\(\left[72.\left(-2\right)\right].\left[-50.\left(-2\right)\right]\)

=-144.100

=-14400

b)=(125.8).(-5).(-20)

=1000.100

=100000

c)=\(\left[125.\left(-4\right)\right]\).(-3).(-32)

=-500.96

=-48000

d)=-492.125

=-60500

a: 262+(2x-123)=283

=>2x-123=283-262=21

=>2x=123+21=144

=>\(x=\frac{144}{2}=72\)

b: \(63-\left(-51+3x\right)=237\)

=>63+51-3x=237

=>114-3x=237

=>3x=114-237=-123

=>x=-41

c: \(-\left(2x+24\right)+211=-123\)

=>-(2x+24)=-123-211=-334

=>2x+24=334

=>2x=310

=>x=155

d: \(125-\left(125-x\right)=0\)

=>125-x=125

=>x=125-125

=>x=0

(1/2+2/3+3/4+4/5+...+122/123+123/124).(125-5.25)

=(1/2+2/3+3/4+4/5+...+122/123+123/124).(125-125)

=(1/2+2/3+3/4+4/5+...+122/123+123/124).0=0

a: \(=63-\left[\left(-111\right)^3:4\right]\cdot27=9231572,25\)

b: =-(33+66)=-99

9 231 572, 25
-99

7875 tick giùm cái cho tròn 20

\(\frac{125\cdot\left(125+1\right)}{2}=7875\)

1 - 1/2 + 1/3 - 1/4 + .. + 1/121 - 1/122 + 1/123

=  ( 1 + 1/3 + ... + 1/121 + 1/123 ) - ( 1/2 + 1/4 + .. + 1/122 ) 

Đến bước này ta sẽ cùng cộng 2 vế với : 1/2 + 1/4 + .. + 1/122 

=   ( 1 + 1/2 + 1/3 + 1/4 + ...+ 1/121 + 1/122 + 1/123 ) - 2. ( 1/2 + 1/4 + .. + 1/122 )

=    (  1 + 1/2 + 1/3 + ...+ 1/122 +1 /123 )  -  (  1 + 1/2 + ...+ 1/61 ) 

=                   1/62 + 1/63 + ..+1/122 + 1/123 

Chúc học giỏi !!